Since one went on okay and the other won't fully seat, check to make sure the parts store provided you with the correct drum.
As far as replacing rear brakes, here is a link that explains how it's done in general. You can use it to help.
If you look below, the directions specific to your vehicle are included. Note they include replacing the wheel cylinder, but that is how they do it in the manual.
Let me know if this helps.
See pics below.
Images (Click to enlarge)
Thursday, October 13th, 2022 AT 9:16 PM